This proposal addresses hemodynamic and cellular mechanisms of impaired angiotensin converting enzyme (ACE) activity and serotonin (5HT) transport/binding in experimental lung injury. Both are properties of endothelial cells (EC) which, in the microvasculature of whole lung, provide a large surface area for interaction with blood. Despite the importance of microvessel EC in the interaction with ACE substrates or 5HT, most mechanistic studies have been with large vessel EC (in culture), often from extra-pulmonary sources. Therefore, we will apply selected drug-induced injury protocols to cultured EC from both large vessel and microvessel origin and the intact lung in order to approach the key question, namely, to what extend can cell culture data be extrapolated to the intact lung and whole animal? Our proposed experiments, with intact lung and EC or large and small vessels, will shown whether, 1) ACE protein synthesis in microvascular EC and whole lung is regulated by glucocorticoid, as proposed for large vessel EC, 2) reduced ACE hydrolytic activity associated with lung-injury reflects inhibition, not of the enzyme, but of the putative glucocorticoid receptor which modulates syntheses of ACE, 3) reduced 5HT transport of drug-induced lung injury reflects a cell action modifying the expression or accessibility of receptor/transporter protein, 4) this effect is functionally linked to edema production in perfused lungs. We will also examine the impact of altered flow, or microvascular EC surface area, on kinetics of endothelial-substrate interaction. For this purpose we will use microcarrier bead-EC columns, superfused at different flow rates in series or parallel networks, which are fixed with respect to both surface area and cell number. Mathematical analysis of these simple initial models will be refined to incorporate data form experiments which will simulate heterogenity of injury by inhibiting ACE in one of two columns perfused in parallel from a common reservoir. This approach will allow us to unravel the complex interaction of endothelial cell damage and accompanying hemodynamic influences.